On June 28, 1914, Archduke Franz Ferdinand, heir to the throne of the Austro-Hungarian empire, his morganatic wife at his side, traveled in a motorcade along the Miljacka River in Sarajevo, capital of the restless province of Bosnia-Herzegovina. Seven conspirators carrying guns, bombs, and suicide pills lined the quay. One of them hurled a bomb at the royal automobile, but it missed its target and struck the car behind, injuring the occupants. Stiff and priggish but undeniably brave, the archduke carried on with the day’s events. After a formal but ironic welcome at the town hall, the motorcade returned along the same quay, the lead driver having been instructed not to turn onto Franz Josef Street, the previously published route. But the archduke’s driver, uninformed of the change, turned as originally planned. When he realized his mistake and stopped the car, another conspirator, a Bosnian Serb named Gavrilo Princip, fired two shots from a few feet away. Minutes later, the royals were dead.

The Sarajevo visit had been ill timed; June 28 is the anniversary of the Battle of Kosovo, in 1389, in which the Ottoman Empire crushed a Serbian uprising and consolidated its rule in the Balkans. By 1914, Austria-Hungary had governed Bosnia for more than four decades, since wresting it away from the Ottomans, but it had formally annexed the province just six years earlier. Neighboring Serbia, which had enlarged and consolidated its territory during the recent Balkan wars, wished to gather fellow Slavs in Bosnia and elsewhere under its own rule. To that end, elements of the Serbian government armed the assassins and dispatched them to Sarajevo.

The assassinations evoked little sympathy; despite his pacific tendencies, the archduke was an unpopular figure at home and abroad. And yet the Sarajevo murders set off an international crisis that led in five weeks to World War I. A peaceful continent at the height of its prestige and cultural influence tore itself to pieces, and liberal civilization suffered a devastating blow.

This diplomatic dance of death is the subject of Sean McMeekin’s gripping and well-researched new book. In prose of admirable clarity, he relates the enormously complex events of that fateful summer. Knowledge of the carnage to come increases the narrative drama; in chancelleries all over Europe, statesmen strolling cool marble floors made decisions that consigned millions to cold, muddy trenches. As Christopher Clark has written in his recent and more compendious account of the 1914 crisis, “causes trawled from the length and breadth of Europe’s pre-war decades are piled like weights on the scale until it tilts from probability to inevitability. Contingency, choice, and agency are squeezed out of the field of vision.” McMeekin concurs and, in his day-by-day and even hour-by-hour account, brings a sprawling cast of characters to life.

Austrian emperor Franz Josef was a survivor; after six decades on the throne, he was wary of war. But his ministers yearned to retaliate against Serbia and bolster the empire’s fading prestige. Chief among the hawks were foreign minister Leopold Berchtold, a late convert to militarism, and General Franz Conrad, the ferociously bellicose army chief of staff. Berchtold wished to efface his reputation for indecisiveness; Conrad wanted desperately to impress his mistress. Such were the motives that helped lead to war. Together they assured their cautious sovereign that, with German help, victory would be swift.

But others feared a wider conflict. The chief obstacle to the plans of the Austrian war party was the Hungarian minister-president, Stefan Tisza. Jealous of his prerogatives as head of government of a coequal half of the empire, and determined to preserve the precarious political advantage enjoyed by his fellow Magyars (which would be threatened if a large population of Slavs were absorbed into the country in a successful war), he bitterly opposed the plans of Berchtold and Conrad. In tense meetings with his Austrian colleagues, he raised every possible objection to war with Serbia. But in McMeekin’s telling, this apostle of peace may have inadvertently contributed to the catastrophe. Left to their own devices, the warlike Austrians might have swiftly committed the empire to a localized conflict with Serbia, attacking Belgrade before the other European powers could react. It might have been just another Balkan spat, of which there had been many.

But it was not to be. Austria-Hungary, before delivering the harshest possible ultimatum to Belgrade, secured a “blank check” for military support from Germany, its sole ally. The mercurial Kaiser Wilhelm II had been close to Franz Ferdinand, and had a vested interest in punishing homicide against royals. A grandson of Queen Victoria, he was related to most of Europe’s sovereigns — George V of England and Tsar Nicholas II of Russia were his cousins. But these blood ties did nothing to prevent bloodshed.

So it was Germany, squeezed uncomfortably between France to the west and Russia to the east, and jealous of its imperial rivals, that gave the Austrians license to pursue revenge. The Treaty of Versailles formally blamed Germany for causing the war, and most historians since have agreed. But McMeekin rejects this: “So far from ‘willing the war,’” he writes, “the Germans went into it kicking and screaming as the Austrian noose snapped shut around their necks.” He disputes the long-dominant Germanocentric interpretation of the war’s outbreak, faulting all the major powers but pouring particular scorn upon the conduct of Russia.

It was the mobilization of that vast country that, McMeekin believes, pushed the world over the brink. The tsar’s regime was brittle; defeat at the hands of Japan a decade before had sparked rebellion, and modest political reform had done little to shore up his rule. But the Russian government felt bound by ties of ethnic kinship to support Serbia, and was lashed to the fortunes of France by formal treaty. A five-day “Period Preparatory to War” saw the Russian war engine stir to life, and, despite its officially preliminary nature, it imposed great strain upon the already desperate diplomacy going on abroad. The sheer relentlessness of the process calls to mind A. J. P. Taylor’s phrase “war by timetable.” And yet human agency played a primary role: Mobilization was briefly halted by the equivocating Nicholas II, who peered into the abyss and cried, “I will not be responsible for a monstrous slaughter!” But this was but a momentary stay of execution. The troops and trains soon moved again, ushering Europe into the abyss.

The British cabinet, vexed as ever by unrest in Ireland, only reluctantly cast their eyes toward the Balkans. Prime minister Herbert Asquith gave foreign minister Sir Edward Grey a free hand in diplomacy, putting the fate of the world in the hands of an aristocrat happier on his estate than in the Foreign Office. An avid outdoorsman and author of the classic Fly Fishing, Grey was suspicious of Germany and partial to France. And, given the Franco-Russian alliance (solidified by a summit, vividly depicted by McMeekin, between the French president and the Russian tsar soon after the Sarajevo murders), British support for France helped ensure war with Germany. Had the foreign secretary been clearer about his commitments, the other powers might have acted more cautiously. But both sides in the rapidly brewing conflict convinced themselves that England would keep out. This was precisely what most of Grey’s Liberal colleagues wished, but Germany’s threat to Belgian territory yielded a British declaration of war. The drafters of the 1839 treaty guaranteeing Belgian neutrality could hardly have imagined the apocalypse that would result.

As Niall Ferguson argued in his brilliant The Pity of War, British restraint might have allowed a swift German victory, the likely result of which would have been German dominance of a European customs union. In other words, a brief continental conflict might have led to a Europe much like the one we know today, without the intervening horrors of Nazism, the Holocaust, and all the other disasters that made the last century the bloodiest. Some look askance upon counterfactuals, but consider the butcher’s bill: 10 million dead, millions more wounded, the rise of Bolshevism with all its attendant horrors, and the festering hatreds that enabled the career of Hitler.

Recent and magisterial histories of the war by Hew Strachan and David Stevenson have tried to invest “The Great War” — as it was known until its savage 1939–45 sequel — with purpose. But the facts speak for themselves: The fumbling statesmen of 1914 ignited a flame that consumed 10 million souls and set the 20th century on a disastrous course. It might have been Germany’s fault; it might have been Russia’s. Whatever the case, the key image is not that of a smoking gun, but that of a circular firing squad. The world’s most sophisticated, interconnected, and technologically advanced civilization destroyed itself. A century later, we still suffer the consequences.

– Mr. Bishop has held several posts on Capitol Hill and in the White House and is the former executive director of the Abraham Lincoln Bicentennial Commission.